1. Field of the Invention
The invention relates to a method and apparatus for sealing cartons by sticking together facing surfaces of a hinged flap and a wall of each carton using a solvent-based adhesive, in particular a water-based adhesive.
2. Description of the Prior Art
For sealing cartons, solvent-based adhesives have significant advantages of cost over known hot melt adhesives and water-based adhesives have a particular advantage in that it is unnecessary to provide for evacuation of the solvent to avoid undesirable environmental effects. However, the known solvent-based adhesives, and particularly water-based adhesives, require a significant drying time, e.g. of the order of 1 second, which has in the past limited the rate of production of sealed cartons using such adhesives.
In our prior British Pat. Specification No. 2,103,145 we have disclosed the use of a spray gun to apply an atomised spray of water-based adhesive to selected parts of the carton, the outlet from the spray gun being a nozzle controlled by a needle valve which cooperates with the nozzle to cause a swirling motion of the atomised spray of adhesive. The sprayed adhesive was partially dried by directing hot gas on to the selected parts which were then pressed against cooperating parts of the blank to seal them together by means means of the partially dried adhesive. The combination of application of the water-based adhesive as an atomised spray with a swirling motion, and its drying by hot air, enabled rapid and effective adhesion of the selected and cooperating parts of the carton to be made, but problems were encountered in practice because the spray nozzles tended to clog and had to be cleared frequently.